On September 5, 2001, approximately 1530 Pacific daylight time a Cessna 172RG, N44EF, registered to and being operated by Aeroflight Executive Services, Inc., and being flown by a commercially rated flight instructor, was substantially damaged during an in-flight collision with trees and terrain while maneuvering approximately five nautical miles east of Carbonado, Washington. The pilot and passenger sustained minor injuries. Visual meteorological conditions prevailed and no flight plan had been filed. The flight was an aerial fire survey and was operated under 14CFR91 originating from Boeing Field, Seattle, Washington, approximately 1400 on the afternoon of the accident. The pilot reported that following the crash; he and his passenger exited the aircraft noting fuel spilling from the left fuel tank and contacted the operator by cell phone advising them of the accident. A search was initiated and the two occupants were found the following morning. The pilot and passenger were both interviewed by an inspector assigned to the Federal Aviation Administration's Flight Standards District Office, Renton, Washington (refer to ATTACHMENTS P-I and P-II). The pilot reported in the interview that he had departed Boeing field with the non-rated passenger and headed towards the intended patrol area. During the flight to the patrol area, he had demonstrated some basic flight maneuvers to the passenger, who had never been in a small aircraft before, and then allowed the passenger to fly the aircraft. The pilot reported that as the passenger, who was occupying the left seat, flew the aircraft the pilot acted as fire spotter. He also recalled that the power was set to 23 inches of manifold pressure and 2,400 rpm and that the aircraft was operating between 3,000 and 4,000 feet above mean sea level. The pilot reported that the ceiling was about a 4,000 to 5,000 foot "ragged overcast" and that he had encountered rain showers earlier in the flight. According to the FAA inspector's interview transcript, the pilot stated that "...While the aircraft was maneuvered along a southeasterly heading into a canyon, [the pilot] noted that the aircraft's performance seemed to be deteriorating. Shortly thereafter, [the pilot] heard the engine start 'coughing,' at which time, he took control of the airplane. [The pilot] stated that there was about a 10 to 15 second period between the time he initially noted the decrease in performance, to when the engine coughing began, and that though he was approximately 1,000 feet above the ground, he was only 200 feet horizontally from the rising terrain...." The pilot reported checking the fuel selector "ON," the mixture control "FULL RICH," the propeller control "FULL FORWARD," and the throttle "FULL OPEN," but this resulted in no change in engine performance. He further reported that there was no time to continue trouble-shooting the problem including "...checking the carburetor heat..." and that at the time of the crash "...it was likely that the engine was still producing power, but not much...." When the FAA inspector asked the pilot what he felt had happened, the pilot stated that "...he probably had encountered carburetor icing..." and that "...the last time he had checked any of his engine instruments was approximately 10 minutes prior to the accident...." The FAA inspector inquired if the pilot had ever encountered carburetor icing and he replied "...he had not...." The pilot was also asked what mountain flying experience training he had received and he replied that "...he had no formal [mountain] flight training, but that he had watched a 'Jeppesen' video on the subject, and that he had given several mountain-flying checkouts himself...." The aviation surface weather observation taken at McCord Air Force base at 1555 on the afternoon of the accident recorded a surface temperature and dew point of 18 degrees and 7 degrees Celsius respectively. The observation site is 323 feet above sea level and lies 28 nautical miles and 260 degrees magnetic west of the accident site (refer to CHART I and DIAGRAM CARB ICE-I). The accident site was fixed using a GPS (global positioning system) unit during the search and rescue. The aircraft was located within a draw along the South Fork of the South Prairie Creek about 2,500 feet above sea level (refer to CHART II). The elevation of the terrain within the canyon rose 2,500 feet along the South Fork axis. The average distance of this terrain rise was approximately 12,000 horizontal feet along the axis, with the last 4,500 feet rising a total of 2,000 feet, a significantly steeper gradient. An FAA inspector interviewed one of the Pierce County Sheriff's deputies who surveyed the accident site (refer to ATTACHMENT INT-I). The deputy reported that the carburetor heat control in the aircraft was found in the "OFF" position (from Pierce County Incident Report No. 01-248-0904). The aircraft was subsequently recovered from the site and transported to Discount Aircraft Salvage, Deer Park, Washington. The aircraft's engine was test run under the supervision of an NTSB investigator, and although the engine operated, a power degradation was noted. Examination and testing of the magnetos revealed that the left Slick magneto's coil was not operating. It could not be determined whether the inoperative magneto was related to impact damage during the crash or pre-existed the impact. The pilot reported to the FAA inspector that prior to takeoff "...all systems appeared to be functioning normally...."